Timber is generally used for making stair stringers, usually by cutting triangles out of a 2".times.10" or 2".times.12" beam to form right-angled recesses for receiving the riser and tread portions of stairs. When stringers are cut out of timber in this fashion, the timber is weakened. Expertise is required to avoid cracks so as not to waste timber. Nevertheless, cracks often do develop in the stringer after the cut-outs have been made. Alternative methods for building stairs have been proposed, such as, for example, a modular carrier for a stair tread as described in U.S. Pat. No. 4,583,334 and a stair bracket, as described in U.S. Pat. No. 4,819,391. However, there is still a need for an effective and inexpensive stair construction unit which is easy to apply and which saves timber and labour costs.